It has been a goal of conventional container design to form container bodies that have a desired and predictable shape after filling and at the point of sale. For example, it is often desired to produce containers that maintain an approximately cylindrical body or a circular transverse cross section. However, in some instances, the containers are susceptible to negative internal pressure (that is, relative to ambient pressure), which causes the containers to deform and lose rigidity and stability, and results in an overall unaesthetic appearance. Several factors can contribute to the buildup of negative pressure inside the container.
For instance, in a conventional hot-fill process, the liquid or flowable product is charged into a container at elevated temperatures, such as 180 to 190 degrees F., under approximately atmospheric pressure. Because a cap hermetically seals the product within the container while the product is at the hot-filling temperature, hot-fill plastic containers are subject to negative internal pressure upon cooling and contraction of the products and any entrapped air in the head-space. The phrase hot filling as used in the description encompasses filling a container with a product at an elevated temperature, capping or sealing the container, and allowing the package to cool.
As another example, plastic containers are also often made from materials such as polyethylene terephthalate (PET) that can be susceptible to the egress of moisture over time. Biopolymers or biodegradable polymers, such as polyhydroxyalkanoate (PHA) also exacerbate egress issues. Accordingly, moisture can permeate through container walls over the shelf life of the container, which can cause negative pressure to accumulate inside the container. Thus, both hot-fill and cold-fill containers are susceptible to the accumulation of negative pressure capable of deforming conventional cylindrical container bodies.
Many conventional cylindrical containers would deform or collapse under the internal vacuum conditions without some structure to prevent it. To prevent collapse, some containers have panels, referred to as “vacuum panels,” located in the body sidewall. The vacuum panels are configured to flex radially inward in response to internal vacuum such that the remainder of the container body remains cylindrical. Although the deflection of the panels enables the remainder of the container to have its desired shape, the area that includes the vacuum panels still undergoes radial deformation, which is not aesthetically or commercially appealing and presents difficulties for labeling.
Thus, it is desirable to provide a hot-fill container capable of providing vacuum compensation structure that flexes in a non-radial direction in response to the accumulation of negative internal pressure.